> Take any phenomena on a globe earth, describe the exact same thing in flat earth coordinates and then say that everything weird in the equations is a new physical effect you just discovered.

You can't actually do that in an internally consistent way. (Or atleast I've never seen it.) It isn't only interally incosistent but those theories also break down if you look at them too closely. That's why so much of flat earthism relies on conspiracy theories that are used to justify ignoring phenomena rather than actually investigating it.